Fuel additives and compositions

ABSTRACT

A salt formed by the reaction of a carboxylic acid with a hydrocarbyl derivative of pyridine. The salts are effective lubricity enhancers when added to low sulphur content fuels and are soluble at low temperatures.

This invention relates to additives, and to their use to improve the characteristics of fuel oils, especially middle distillate fuels such as diesel fuels, kerosene and jet fuel.

Environmental concerns have led to a need for fuels with reduced sulphur content, especially diesel fuel, heating oil and kerosene. However, the refining processes that produce fuels with low sulphur contents also result in a product of lower viscosity and a lower content of other components in the fuel that contribute to its lubricity, for example, polycyclic aromatics and polar compounds. Furthermore, sulphur-containing compounds in general are regarded as providing some anti-wear properties and a result of the reduction in their proportions, together with the reduction in proportions of other components providing lubricity, has been an increase in the number of reported problems in fuel pumps in diesel engines. The problems are caused by wear in, for example, cam plates, rollers, spindles and drive shafts, which may result in sudden pump failures relatively early in the life of the engine.

The problems may be expected to become worse in future because, in order to meet stricter requirements on exhaust emissions generally, higher pressure fuel systems, including in-line, rotary pumps, common-rail pumps and unit injector systems, are being introduced, these being expected to have more stringent lubricity requirements than present equipment, at the same time as lower sulphur levels in fuels become more widely required.

Historically, the typical sulphur content in a diesel fuel was below 0.5% by weight. In Europe maximum sulphur levels have been reduced from 0.20% to 0.05% and in Sweden grades of fuel with levels below 0.005% (Class 2) and 0.001% (Class 1) are in use. A fuel oil composition with a sulphur level below 0.05% by weight is referred to herein as a low-sulphur fuel.

Such low-sulphur fuels may contain an additive to enhance their lubricity. These additives are of several types. In WO 94/17160, there is disclosed a low sulphur fuel comprising a carboxylic acid ester to enhance lubricity, more especially an ester in which the acid moiety contains from 2 to 50 carbon atoms and the alcohol moiety contains one or more carbon atoms. In U.S. Pat. No. 3,273,981, a mixture of a dimer acid, for example, the dimer of linoleic acid, and a partially esterified polyhydric alcohol is described for the same purpose. In U.S. Pat. No. 3,287,273, the use of an optionally hydrogenated dimer acid glycol ester is described. Other materials used as lubricity enhancers, or anti-wear agents as they are also termed, include a sulphurized dioleyl norbornene ester (EP-A-99595), castor oil (U.S. Pat. No. 4,375,360 and EP-A-605857) and, in methanol-containing fuels, a variety of alcohols and acids having from 6 to 30 carbon atoms, acid and alcohol ethoxylates, mono- and di-esters, polyol esters, and olefin-carboxylic acid copolymers and vinyl alcohol polymers (also U.S. Pat. No. 4,375,360).

Such additives are commonly provided in the form of additive compositions where the active species is dissolved in a solvent, optionally together with other additives. Although largely effective as lubricity additives, it has been found that certain carboxylic acids and carboxylic acid esters, as well as other known lubricity additives, have the disadvantage of poor solubility at low temperature. This poor solubility is found in relation to the solvents used to provide additive compositions (normally hydrocarbon based), and also in relation to the fuels into which the additive is added. This places a limitation on the storage and use of certain known lubricity additives at low ambient temperatures.

U.S. Pat. No. 6,328,771 describes the use of the product of the reaction between a carboxylic acid and a heterocyclic aromatic amine to improve the lubricity of a low sulphur content fuel oil. Examples of heterocyclic aromatic amines include pyridine, pyrazine, pyrolle, pyrazole and imidazole, with imidazole being particularly preferred.

EP 0 798 364 A1 describes the use of a salt formed by the reaction between a carboxylic acid and an aliphatic amine to improve inter alia, the lubricity of a diesel fuel.

The present invention is based on the discovery of novel salts derived from hydrocarbyl derivatives of pyridine, and the observation that such salts, when added to a fuel oil, improve the lubricity thereof. It is a further advantage that the salts of the invention have greatly improved low temperature solubility when compared to more conventional lubricity enhancers. It is also an advantage that the salts of the invention have relatively high flash points, compared to for example, the salts described in U.S. Pat. No. 6,328,771. This leads to benefits in terms of the ease of, and hazards associated with, their handling and transportation.

Thus in accordance with a first aspect, the present invention provides a salt formed by the reaction of a carboxylic acid with a hydrocarbyl derivative of pyridine.

In this specification, the use of the term ‘salt’ to describe the product formed by the reaction of the carboxylic acid and the derivative of pyridine should not be taken to mean that the reaction necessarily forms a pure salt. It is presently believed that the reaction does form a salt and thus that the reaction product contains such as salt however, due to the complexity of the reaction, it is likely that other species will also be present. The term ‘salt’ should thus be taken to include not only the pure salt species, but also the mixture of species formed during the reaction of the carboxylic acid and the hydrocarbyl derivative of pyridine.

Preferably, the hydrocarbyl derivative of pyridine is represented by the formula:

wherein n is an integer between 1 and 5; and wherein each R independently represents a hydrocarbyl group having between 1 and 30 carbon atoms.

Preferably, n is at least 2.

Preferably, each R independently represents a hydrocarbyl group having between 1 and 15 carbon atoms, more preferably, between 1 and 8 carbon atoms.

As used in this specification, the term ‘hydrocarbyl’ refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon character. Among these, there may be mentioned aliphatic groups such as alkyl and alkenyl groups. Such groups may be saturated or unsaturated, linear or branched. The groups may also contain non-hydrocarbon substituents provided their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbon group is substituted, a single (mono) substituent is preferred. The groups may also or alternatively contain atoms other that carbon in a chain otherwise composed of carbon atoms. Suitable hetero atoms include for example, nitrogen, oxygen or sulphur.

Preferably, at least one group R represents an alkyl or alkenyl group. The following structures are representative of the types of species contemplated as hydrocarbyl derivatives of pyridine. These are included merely to illustrate the present invention and are not to be considered limiting in any way.

The hydrocarbyl derivative of pyridine may be used as a single species or as a mixture of two or more different species in any ratio. A suitable commercial source of hydrocarbyl derivatives of pyridine are ‘Alkolidine’ products available from Lonza Ltd.

As carboxylic acid, those corresponding to the formula [R′(COOH)_(x)]_(y), where each R′ is independently a hydrocarbon group of between 2 and 30 carbon atoms, and x is an integer between 1 and 4, are suitable. Preferably, R′ is a hydrocarbon group of 8 to 24 carbon atoms, more preferably, 12 to 20 carbon atoms. Preferably, x is 1 or 2, more preferably, x is 1. Preferably, y is 1, in which case the acid has a single R′ group. Alternatively, the acid may be a dimer, trimer or higher oligomer acid, in which case y will be greater than 1 for example 2, 3 or 4 or more. R′ is suitably an alkyl or alkenyl group which may be linear or branched. Examples of carboxylic acids which may be used in the present invention include: lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, neodecanoic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, caproleic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, coconut oil fatty acid, soy bean fatty acid, tall oil fatty acid, fish oil fatty acid, rapeseed oil fatty acid, tallow oil fatty acid and palm oil fatty acid. Mixtures of two or more acids in any proportion are also suitable. Also suitable are the anhydrides of carboxylic acids and mixtures thereof. In a preferred embodiment, the carboxylic acid comprises tall oil fatty acid (TOFA). It has been found that TOFA with a saturate content of less than 5% by weight is especially suitable. Preferably, TOFA with a abietic acid content of less than 5% by weight, for example, less than 2% by weight, is used.

In another preferred embodiment, the carboxylic acid comprises soy bean fatty acid (SOFA).

Also suitable are aromatic carboxylic acids and their alkyl derivatives as well as aromatic hydroxy acids and their alkyl derivatives. Illustrative examples include benzoic acid, salicylic acid and acids derived from such species.

Preferably, the carboxylic acid has an iodine value of at least 100 g/100 g, more preferably at least 130 g/100 g, for example, at least 150 g/100 g. This has been found to further improve the low temperature solubility of the salts of the invention.

Preferably, the salt has a flash point of at least 50° C., more preferably at least 60° C.

The salt may conveniently be produced by mixing the carboxylic acid with the hydrocarbyl derivative of pyridine. The order in which one component is added to the other is not important. The molar ratio of the amount of acid to the amount of hydrocarbyl derivative of pyridine is preferably from 10:1 to 1:10, more preferably from 10:1 to 1:2, for example, around 1:1. The reaction may be conducted at room temperature, but is preferably heated gently, for example to 40° C.

In accordance with a second aspect, the present invention provides an additive composition comprising a salt according the first aspect.

Additive compositions according to the invention advantageously contain between 3 and 85%, preferably between 10 and 75%, more preferably between 10 and 50%, for example between 10 and 40% of the salt in an oil or a solvent miscible with oil.

A composition comprising the salt in admixture with a suitable solvent is convenient as a means for incorporating the salt into bulk oil such as distillate fuel, which incorporation may be done by methods known in the art. The compositions may also contain the other additives as required. Examples of solvents are organic solvents including hydrocarbon solvents, for example petroleum fractions such as naphtha, kerosene, diesel and heater oil; aromatic hydrocarbons such as aromatic fractions, e.g. those sold under the ‘SOLVESSO’ tradename; alcohols and/or esters; and paraffinic hydrocarbons such as hexane and pentane and isoparaffins. The solvent must, of course, be selected having regard to its compatibility with the salt and with the oil and/or fuel.

The additive compositions of the invention are particularly stable at low temperatures. Preferably, the additive composition is such that a 75 wt % solution of the salt in a hydrocarbon solvent remains clear and bright when held at −30° C. for 28 days. More preferably, a 75 wt % solution of the salt in a hydrocarbon solvent remains clear and bright when held at −40° C. for 28 days.

In accordance with a third aspect, the present invention provides a fuel oil composition comprising a major amount of a fuel oil and a minor amount of a salt according to the first aspect or an additive composition according to the second aspect.

Preferably, the oil is a fuel oil, e.g., a petroleum-based fuel oil, especially a middle distillate fuel oil. Such distillate fuel oils generally boil within the range of from 110° C. to 500° C., e.g. 150° C. to 400° C. The fuel oil may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and thermally and/or refinery streams such as catalytically cracked and hydro-cracked distillates. The most common petroleum distillate fuels are kerosene, jet fuels, diesel fuels, heating oils and heavy fuel oils. The heating oil may be a straight atmospheric distillate, or it may contain minor amounts, e.g. up to 35 wt %, of vacuum gas oil or cracked gas oil or of both.

Other examples of fuel oils include Fischer-Tropsch fuels. Fischer-Tropsch fuels, also known as FT fuels, include those described as gas-to-liquid (GTL) fuels, biomass-to-liquid (BTL) fuels and coal conversion fuels. To make such fuels, syngas (CO+H₂) is first generated and then converted to normal paraffins by a Fischer-Tropsch process. The normal paraffins may then be modified by processes such as catalytic cracking/reforming or isomerisation, hydrocracking and hydroisomerisation to yield a variety of hydrocarbons such as iso-paraffins, cyclo-paraffins and aromatic compounds. The resulting FT fuel can be used as such or in combination with other fuel components and fuel types such as those mentioned in this specification.

Preferably, the fuel oil has a sulphur content of at most 0.2% by weight, more preferably of at most 0.05% by weight, especially of at most 0.035%, for example, at most 0.015%. Fuels with even lower levels of sulphur are also suitable such as, fuels with less than 50 ppm sulphur by weight, preferably less than 20 ppm, for example 10 ppm or less.

Preferably, the salt is present in the fuel oil at a level of between 5 and 1000 ppm by weight, more preferably between 10 and 500 ppm, even more preferably between 10 and 250 ppm, especially between 10 and 150 ppm, for example, between 50 and 150 ppm.

In accordance with a fourth aspect, the present invention provides the use of a salt according to the first aspect, or of an additive according to the second aspect, to improve the lubricity of a fuel oil having a sulphur content of less than 0.2% by weight.

The salt of the invention may be used singly or as a mixture of more than one salt. It may also be used in combination with one or more co-additives such as are known in the art, for example the following: detergents, antioxidants (to avoid fuel degradation), corrosion inhibitors, dehazers, demulsifiers, metal deactivators, antifoaming agents, cetane improvers, co-solvents, package compatibilisers, reodourants, additives to improve the regeneration of particulate traps, middle distillate cold flow improvers and other lubricity additives.

The invention will now be described by way of example only.

EXAMPLE 1

In this example, the hydrocarbyl derivative of pyridine used was Alkolidine 10 which is a product of Lonza Ltd and is a mixture of several hydrocarbyl derivatives of pyridine.

Alkolidine 10 (17.0 g, 95 mmoles) was added to a beaker and heated to 40° C. with stirring. Tall oil fatty acid, with a saturate content of ca. 2% and a rosin acid content of ca. 1%, (TOFA) (25.4 g, 88 mmoles) was then added to the beaker. An exotherm of ca. 12° C. was measured indicating that the two components reacted. FTIR analysis of the reaction product showed a reduction in the strong carboxylic acid peak at 1710 cm⁻¹ compared to the starting acid, and a corresponding appearance of carboxylate peaks at 1560 and 1458 cm⁻¹ as well as the appearance of a broad peak at 1935 cm⁻¹ assignable to a pyridinium species. This was a clear indication of the formation of a salt. The flash-point of the reaction product was 116° C.

EXAMPLE 2

Example 1 was repeated using Alkolidine 10 (17.0 g, 95 mmoles) and tall oil fatty acid, with a saturate content of ca. 2% and a rosin acid content of ca. 2%, (TOFA) (25.4 g, 88 mmoles). An exotherm of ca. 12° C. was measured indicating that the two components reacted. FTIR analysis of the reaction product showed a reduction in the strong carboxylic acid peak at 1710 cm⁻¹ compared to the starting acid, and a corresponding appearance of carboxylate peaks at 1560 and 1458 cm⁻¹ as well as the appearance of a broad peak at 1935 cm⁻¹ assignable to a pyridinium species. This was a clear indication of the formation of a salt. The flash-point of the reaction product was 116° C.

EXAMPLE 3 (COMPARATIVE)

Example 1 was repeated using pyridine (87.6 g, 1107 mmoles) in place of Alkolidine 10 and the same TOFA (320 g, 1107 mmoles). An exotherm was again detected indicating that the two components reacted. The flash-point of the reaction product was 46° C.

EXAMPLE 4 (COMPARATIVE)

Example 2 was repeated using pyridine (87.6 g, 1107 mmoles) in place of Alkolidine 10 and the same TOFA (320 g, 1107 mmoles). An exotherm was again detected indicating that the two components reacted. The flash-point of the reaction product was 46° C.

HFRR Testing

The salts prepared in Examples 1 and 2 above were tested in Mk 1 diesel (<10 ppm S) using the High Frequency Reciprocating Rig (HFRR) test in accordance with BS EN ISO 12156-1 (2000). Results are given in Table 1 below together with results of similar tests using Comparative Examples 3 and 4. TABLE 1 Treat Average Treat Average rate/ wear rate/ wear ppm scar/μm ppm scar/μm Base 0 649 Base 0 661 fuel fuel Example 1 50 668 Comparative 50 667 100 499 Example 3 100 538 150 470 150 487 200 406 200 436 250 420 250 422 300 446 300 343 Example 2 50 675 Comparative 50 670 100 611 Example 4 100 515 150 511 150 475 200 467 200 451 250 424 250 380 300 404 300 428

The results indicate that the lubricity performance of the salts of the invention is comparable to that found for simple pyridine salts such as those described in U.S. Pat. No. 6,328,771.

Stability Testing

Additive concentrates of the salts of Examples 1 and 2 were made up as 10, 33, 50 and 75% solutions in Solvesso 100 and tested for low temperature stability at −30° C. and −40° C. alongside similar solutions of Comparative Examples 3 and 4. The non-diluted salts were also tested (100% concentration). The results are given in Table 2 below. In the table, the data refer to the number of days that the test sample remained clear and bright. All tests were run for a maximum of 28 days, so a result of ‘28’ in the Table does not indicate a failure on day 28. TABLE 2 Additive Temper- Compar- Compar- concen- ature/ Example Example ative ative tration ° C. 1 2 Example 3 Example 4 10% −30 28 28 3 28 −40 28 28 0 1 33% −30 28 28 0 0 −40 7 28 0 0 50% −30 28 28 0 0 −40 7 28 0 0 75% −30 14 28 0 0 −40 2 28 0 0 100% −30 6 28 0 0 −40 0 0 0 0

It is clear from the results given in Table 2 that the low temperature stability of the salts of the present invention far exceeds that found for simple pyridine salts such as those described in U.S. Pat. No. 6,328,771. 

1. A salt formed by the reaction of a carboxylic acid with a hydrocarbyl derivative of pyridine.
 2. A salt according to claim 1, wherein the hydrocarbyl derivative of pyridine is represented by the formula:

wherein n is an integer between 1 and 5; and wherein each R independently represents a hydrocarbyl group having between 1 and 30 carbon atoms.
 3. A salt according to claim 2, wherein n is at least
 2. 4. A salt according to claim 2, wherein at least one group R represents an alkyl or alkenyl group.
 5. A salt according to claim 3, wherein at least one group R represents an alkyl or alkenyl group.
 6. A salt according to claim 1, wherein the carboxylic acid comprises a fatty acid or a mixture of fatty acids.
 7. A salt according to claim 6, wherein the carboxylic acid comprises tall oil fatty acid (TOFA).
 8. An additive composition comprising a salt according to claim
 1. 9. A fuel oil composition comprising a major amount of a fuel oil and a minor amount of a salt according to claim
 1. 10. A fuel oil composition comprising a major amount of a fuel oil and a minor amount of an additive composition according to claim
 8. 11. A fuel oil composition according to claim 9, wherein the fuel oil has a sulphur content of less than 0.05% by weight.
 12. A fuel oil composition according to claim 10, wherein the fuel oil has a sulphur content of less than 0.05% by weight.
 13. A method of improving the lubricity of a fuel oil having a sulphur content of less than 0.05% by weight, which method comprises the addition to said fuel oil of a salt according to claim
 1. 14. A method of improving the lubricity of a fuel oil having a sulphur content of less than 0.05% by weight, which method comprises the addition to said fuel oil of an additive composition according to claim
 8. 